Due to recent exhaustion of frequency resources, cognitive radio technology is being continuously developed to satisfy demands of government and industry, which attempt to efficiently use frequency bands.
A licensed user in the existing communication system has a privileged use right to a specific band, and performs communication under that right. Thus, the licensed user can temporally and constantly occupy the specific band, and, in this situation, channel switching is performed in a previously licensed band so that the privileged use right remains guaranteed with respect to a channel to be switched to. Unlike the existing communication system, one or more embodiments of the present invention are related to using cognitive radio technology according to an open spectrum policy in which the privileged use right is not guaranteed. Hereinafter, with respect to cognitive radio systems, for convenience of description, the licensed user is referred to as an ‘incumbent user (IU)’.
Cognitive radio technology randomly or periodically scans or senses whether the IU uses a corresponding band, thereby using a band that is currently not used by the IU. Also, the cognitive radio technology periodically scans whether the IU enters the corresponding band during usage of the corresponding band. If the IU enters the corresponding band, the cognitive radio technology discontinues data transmission and reception, switches its communication channel to another band free from the IU, and re-establishes the discontinued data transmission and reception, thereby maintaining communication. That is, a core of the cognitive radio technology is a channel switching procedure in which entrance of the IU is sensed so that communication in a corresponding band is discontinued and a communication channel is switched to another band free from the IU.
In the case of the Institute of Electrical and Electronics Engineers (IEEE) 802.11h standard, the cognitive radio technology is partially used to operate a wireless local area network (WLAN) system in a 5 GHz band in which a radar signal and a satellite signal are Ws. At this time, since the IUs perform transmission to a wider area by using relatively large power, the cognitive radio technology is used in a simple manner. An IEEE 802.22 Wireless Regional Area Network (WRAN) system is considered as an initial standard based on the cognitive radio technology, and is a system that basically operates in an Ultra High Frequency (UHF) band in which a television (TV) signal and a Wireless Micro Phone (WMP) signal are IUs. Standardization work with respect to the IEEE 802.22 WRAN system is currently being conducted and, in regard to initialization after channel switching, an alternative technology is not yet been developed. In the IEEE 802.11h standard, each access point (AP) after channel switching is designed to re-set a channel from the beginning.
In the cognitive radio system, when communication in an operational channel is determined to be discontinued due to the IU entering the operational channel that is currently being used or due to an excessive interference occurring in the operational channel, the operational channel is switched to a pre-arranged channel. However, since some parameters are different between the operational channel and the pre-arranged channel, an initialization procedure has to be performed to allow the cognitive radio system to be adapted to those different parameters. Since an initialization technique aiming for this situation has not been developed yet, a conventional cognitive radio system uses a general initialization technique used to initially operate a system. However, the general initialization technique has to allow the system to be adapted to many parameters so that it takes a relatively long initialization time.
Accordingly, there is a demand for a technology capable of rapidly performing initialization work after channel switching is performed in the cognitive radio system.